Electrical signals recorded or measured from a living subject are often used as predictors and/or indicators of the state of a physiological system. In some cases, such signals are recorded to measure the response of the subject to another stimulus signal. For example, vestibular evoked myogenic potentials (VEMPs) are electrical signals recorded from the skin overlying skeletal muscles of the head and neck in response to high-intensity acoustic stimuli. Such signals, however, are characterized by a high degree of variability that depends on various factors including when and where on the skin the signal is being measured and the condition of the subject. The measured signals are also affected by noise from other physiological processes. Thus, signals measured from a living body generally cannot be used as a reliable indicator of a physiological process.